Plate fin heat exchangers generally consist of a core formed of a plurality of stacked layers. Each layer has a plurality of continuously corrugated or finned elements which are arranged to form a plurality of channels. The channels in one layer may lie in transverse or parallel relation to the channels formed in adjacent layers. A parting sheet separates the adjacent layers. Fluids having differing amounts of heat energy flow through the channels of adjacent layers so that heat energy may be transferred from fluid to fluid. Closure bars, which isolate the fluids, are generally mounted on the sides of each layer parallel to the channels therein. Top and bottom sheets and reinforcing bars may be required to structurally support the core. A typical heat exchanger construction is shown in U.S. Pat. No. 3,365,129 assigned to the assignee of this application.
Environmental control systems (ECSs), which utilize air cycle machines, are well known. Such systems generally control the temperature and humidity of air within an enclosed environment such as an aircraft cabin. An air cycle ECS generally includes; a compressor for pressurizing air input thereto, and a turbine for driving the compressor and for expanding and cooling the air. Some turbines are capable of delivering air at temperatures as low as 100.degree. F. below zero. At such cold temperatures, moisture within the air is precipitated out in the form of snow or ice. The snow and ice may clog and shut down any downstream components, such as heat exchangers. If a heat exchanger becomes clogged, heat transfer among the fluids flowing therethrough may be severely reduced. The air from the turbine may not warm to useable levels for other downstream components The fluid, which warms the air from the turbine in the exchanger, may not be cooled enough for effective downstream use.
Prior art plate fin heat exchangers have difficulty in such extremely cold environments because of clogging due to ice and snow, and cold spots in the heat exchanger core. Accordingly, a plate fin heat exchanger for use in extremely cold environments is sought.